Break up the chocolate and melt in the top of a double saucepan or in the microwave.
Sift together the flour, baking soda and baking powder.
Put the sugar, butter, eggs and vanilla extract into a food processor and process until the mixture is light and creamy. Add the cold chocolate mixture and process to mix.
Sprinkle the flour mixture on top of the creamed mixture with the buttermilk and pulse to mix. Do not over process!
Pour the mixture evenly into 2 well greased floured and lined 23cm cake tins.
Bake at 180° for 35 to 45 minutes until the cake is cooked.
Cool in the tin for 10 minutes before turning out onto a cake rack to cool.
Split each cake in half horizontally. Layer with quarter of the chocolate butter icing and a third of the whipped cream, finishing with a layer of chocolate butter icing and decorate with walnuts or strawberries.

Chocolate butter icing

1. Mix the hot water, cocoa and vanilla extract together and set aside until very cool. Beat together the cocoa mixture, butter and sifted icing sugar.
2. Whip cream until thick and sweeten if wished.
Used with permission from Allyson Gofton - The Great New Zealand Baking Book.